The airline transport pilot was departing in a wheel/ski-equipped airplane, in support of a sled dog race, with one passenger and cargo aboard. The pilot described wind conditions at the time of the accident as gusts to 20 knots, and that the direction was variable. She reported that just after takeoff from the soft, snow-covered frozen lake, and while making a slight left turn, the airplane descended at the departure end of the site, subsequently impacting snow-covered terrain. As a result, the airplane nosed over, sustaining substantial damage to the wings and fuselage. There were no reported mechanical problems with the airplane prior to the accident. In the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) submitted by the pilot, the estimated gross weight of the airplane at takeoff was 3,000 pounds, or approximately 250 pounds below the maximum takeoff gross weight of 3,250 pounds.